The present application claims priority and contains subject matter related to Japanese Patent Applications No. 2000-400698, and No. 2001-366526 filed in the Japanese Patent Office on Dec. 28, 2000 and Nov. 30, 2001, respectively, and the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a sheet feeding device for use in image forming apparatuses, such as copying machines, printers, facsimile apparatuses, printing apparatuses, etc., and an image forming apparatus using the sheet feeding device.
2. Discussion of the Background
In sheet feeding devices for image forming apparatuses, various methods have been proposed for separating stacked sheets so as to be fed one by one. A friction separation method is one of the well known methods. A sheet feeding device using a friction separation method generally includes a feeding roller which rotates in a sheet feeding direction, a separation roller which is pressed against the feeding roller and which is driven, via a torque limiter, to rotate in a direction opposite the sheet feeding direction, and a conveying roller arranged downstream of the feeding roller and the separation roller in the sheet feeding direction. When one sheet is sandwiched between the feeding roller and the separation roller, the separation roller is rotated by rotation of the feeding roller via the torque limiter, and when two or more sheets are sandwiched between the feeding roller and the separation roller, the sheets are separated from each other so as to be fed one by one because the separation roller is rotated in the opposite direction relative to the sheet feeding direction.
In a sheet feeding device using a friction separation method, driving a feeding roller, a separation roller and a conveying roller with individual driving sources is not desirable because of cost. Therefore, a feeding roller, a separation roller and a conveying roller is usually driven with a single driving source. Each of the rollers is connected or disconnected from the single driving source using, for example, an electromagnetic clutch and a solenoid. However, in an electric clutch, an inferior operation of the sheet feeding device may occur depending upon the amount of driving load for the connection and/or the disconnection, by variation in the periods of connection and/or disconnection of the driving source with each of the rollers with the electric clutch or by slippage in the clutch. This adversely influences the sheet conveying property of the sheet feeding device and causes sheet jamming in the sheet feeding device.
The above-described disadvantage in using an electric clutch in a sheet feeding device is addressed in Japanese Patent Laid-open Publication No. 8-59000. In JP No. 8-59000, a plurality of sheet feeding devices are provided in multiple-stages, and each of the sheet feeding devices includes an individual sheet feeding unit. Further, in the sheet feeding unit, a feeding roller, a separation roller, and a conveying roller are driven using a mechanical clutch (such as a one-way clutch) by switching a single reversible motor between forward and reverse directions. Specifically, the feeding, separation and conveying rollers are driven when the motor rotates in the forward direction, and only the conveying roller is driven at a high speed when the motor rotates in the reverse direction. Additionally, in the sheet feeding device of JP No. 8-59000, because the separation roller is stopped together with the feeding roller when rotation of the motor is reversed, if a subsequent sheet is stuck to a part of a sheet being fed (due to static electricity, etc.), the subsequent sheet may be fed together with the sheet being fed, resulting in a so-called double feeding of sheets.
Accordingly, one object of the present invention, is to solve the above-noted and other problems.
Another object of the present invention is to provide a novel sheet feeding device and image forming apparatus that includes a driving force transmitting mechanism that does not use an electric clutch and avoids double feeding of sheets.
To achieve these and other objects, the present invention provides a novel sheet feeding device including a sheet tray configured to accommodate stacked sheets, and a feeding unit configured to feed the stacked sheets in the sheet tray one by one. The sheet feeding unit includes a feeding roller configured to be driven to rotate in a sheet feeding direction in which each of the stacked sheets is fed, and a separation roller configured to be pressed against the feeding roller when feeding each of the sheets and to be driven to rotate, via a torque limiter, in a direction opposite the sheet feeding direction. The separation roller is rotated by rotation of the feeding roller in the sheet feeding direction when a single sheet of the stacked sheets is sandwiched between the feeding roller and the separation roller. The sheet feeding unit further includes a conveying member arranged downstream from the feeding roller in the sheet feeding direction, a driving source configured to drive the feeding roller, the separation roller, and the conveying member, and a driving force transmission mechanism configured to transmit a driving force to each of the feeding and separation rollers and the conveying member such that the separation roller and the conveying member are driven in conjunction with each other.
The present invention also provides an image forming apparatus using the above-noted sheet feeding device or a plurality of sheet feeding devices.